1. Field of the Invention
The present invention relates generally to pumps and, more particularly, to a positive displacement pump having a peripheral inlet to facilitate handling viscous fluids.
2. Description of the Prior Art
Positive displacement pumps capable of recovering oil from depths up to 10,000 feet are typically sucker rod pumps equipped with a plunger, travelling ball valve and standing ball valve. The delivery of the oil or other well fluids to the surface occurs only on the upstroke of the plunger, and production ceases as the plunger lowers for another charge. For higher production rates, there are double-acting piston pumps which can be operated up to depths of 18,000 feet. Delivery of the well fluid to the surface occurs on both the upstroke and the downstroke of the piston, which requires an intake port both at the top and at the bottom of the pump. However, the need to bypass fluid around the ball valve and piston on the downstroke of the piston requires intricate manifolding which complicates the architecture of the pump. The resulting constricted inlet passages are subject to vaporlock stall and cavitation damage.
Thus, a bottom hole double-acting piston pump which provides larger and more efficient intake passages and ports for the efficient intake of well fluids under a wide range of well conditions would be of great value.
U.S. Pat. No. 4,386,889 issued on June 7, 1983, to the inventor herein, discloses a positive displacement pump comprising an enclosure having parallel walls and a plurality of concentric annular rings reciprocatably mounted therebetween. By reciprocating the rings in a predetermined sequence, fluid is caused to flow through a series of inwardly or outwardly propagating chambers defined by the rings